Question in the title.
When is it more beneficial to get a BoRK over a BT? When is it more beneficial to get Liandry's vs Void Staff?
What is the math behind AD damage? Like when does a Last Whisper start to become crucial?
Any and all advice is appreciated! :)
Specific champions function better with certain items.
Graves, Jinx, Draven are examples of ADCs that function better with BT than BoRK. The reason is they have better AD scalings, and their own attack speed steroids that they can utilize in addition to their typical builds.
Vayne, Lucian, and Kalista are ADCs that scale better with attack speed. Vayne gets her %hp true damage proc on every third attack, Kalista stacks more spears, Lucian's ultimate scales harder with attack speed. These champions also lack an attack speed steroid.
As to the Liandry's vs Void Staff. I find that these two are improper substitutes, typically if I'm playing a champion that builds Liandry's they also often want a void staff. Nasreth mentioned that the Liandry's burn is reduced by magic resist and he's correct. So you'd want that extra penetration for it against tanks anyway.
bt is better for reksai, and riven, because with proper build bruiser reksai can deal 1K true damage per W
I can only answer the first two because I'm not very good with Math. In both cases it depends on who you'll be attacking and how quickly you'd like to kill them. The percentage damage is not rue damage in both cases so Armor and Magic Resist can reduce however with it, you get a vague estimate oh long it will take to kill the enemy. Like say the 10% damage on AA from BotRK, you know for a fact that the target is dying in at least 6-10 hits accounting for your normal AA damage and the reduction of the % damage. Now while this can be nice you also have to account for the fact that BT offers more damage, lifesteal and a shield which makes for a unexpected situations and can kill a target in less time than BotRK if they have a low HP pool. Now the key difference is right there. HP pool. If they have high hp then % damage can get the job done much faster, if they're low then BT is much better as % damage is much lower than the flat AD from BT. The same applies to Liandry's. So basically if you want to take down tanks with ease % damage is your go to. Low hp squishies flat damage. You can always however build both if you have the gold for it and the game is in your favour. I'm sorry if my answer has any mistakes by the way, I didn't have much to time type a solid response but I hope it's understandable and it helps.
well %hp is better when there's lots of tanks on the other team
BOTRK is for adcs that need attackspeed to prok a ability like kalista or vayne that are tank busters
BT is for just about every other adc that dosent have something they need to prok draven and jinx are reat examples
Liandry's is for most mages that have a lasting damage effect like brand or need to get into the thick of things like kat
void staff is for basicly every other mage that dosent need to get close to do damage put need that magic pen
and i dont really know that entirety of the math behind attack damage but i know crits do 200% damage unless you have IE but last whisper is basicly always going to be your second last or last item
Liandry's burn is reduced heavily by magic resist so I would only grab it before your Void if you're against a team stacking health with zero MR items (even an Aegis). Thing is most of the time you want to be focusing carries over tanks so the damage from Liandry's won't really help you that much in a straight up teamfight and is most useful in poke/sieging.
BotRK is a situational pickup that's mostly useful for the active ability. Core items for 90% of ADCs are IE + PD/Shiv + LW and by the time you have these 3 items you do enough damage to tanks that your 4th item should be focused on surviving more than damage. BT is great for sustain, especially against thornmail tanks. BotRK is great for escaping assassins or other diving champions due to the active. I would focus more on that than worrying about the damage you're dealing with it.
